I recently obtained a Mac Pro desktop for the office, with a widescreen Samsung 24″ monitor. This Mac Pro has a quad-core Xeon processor, which allows 64-bit instructions. The Xeon is in a 45nm process.
I am very impressed with how quiet the machine is. I cannot hear a fan or feel any vibration. The unit feels cool to the touch even after hours of running. The odd-looking handles on top are convenient, as I found out when shoving the unit under my desk.

The “Leopard” OS (OS X 10.5.whatever) is easy to use. I don’t know if there is an equivalent of CTRL-ALT-DEL on a MAC OS. Hopefully I will never have to find it.
The keyboard is a slim aluminum. I don’t think is comfortable for long term use, though it sure looks pretty. The mouse uses Apple’s one button feature, with a cute little trackball on top, about the size of a pencil eraser. It is hard to get used to the lack of right mouse button. I end up using the apple key shortcuts for copy and paste a lot.
I am using the Samsung monitor in 1920×1080 format. The extra screen space was unbelievable at first, but it didn’t long before I filled it up with open windows. I don’t think I will be able to go back to a standard sized display anytime soon!